A number of technologies presently exist for the rapid creation of models, prototypes, and objects (“parts”) for limited run manufacturing. These technologies are generally called Solid Freeform Fabrication techniques, and are herein referred to as “SFF.” Some SFF techniques include stereolithography, selective deposition modeling, laminated object manufacturing, selective phase area deposition, multi-phase jet solidification, ballistic particle manufacturing, fused deposition modeling, particle deposition, laser sintering, film transfer imaging, and the like. Generally in SFF, complex parts are produced from a build material in an additive fashion as opposed to conventional fabrication techniques, which are generally subtractive in nature. For example, in most conventional fabrication techniques material is removed by machining operations or shaped in a die or mold to near net shape and then trimmed. In contrast, additive fabrication techniques incrementally add portions of a build material to targeted locations, layer by layer, in order to build a complex part. SFF technologies typically utilize a computer graphic representation of a part and a supply of a build material to fabricate the part in successive layers.
SFF technologies have many advantages over conventional manufacturing methods. For instance, SFF technologies dramatically shorten the time to develop prototype parts and can produce limited numbers of parts in rapid manufacturing methods. They also eliminate the need for complex tooling and machining associated with conventional subtractive manufacturing methods, including the need to create molds for custom applications. In addition, customized parts can be directly produced from computer graphic data (e.g., computer-aided design (CAD) files) in SFF techniques.
Generally, in most techniques of SFF, structures are formed in a layer by layer manner by solidifying or curing successive layers of a build material. For example, in stereolithography a tightly focused beam of energy, typically in the ultraviolet radiation band, is scanned across sequential layers of a liquid photopolymer resin to selectively cure resin of each layer to form a multilayered part. In selective laser sintering, a tightly focused beam of energy, such as a laser beam, is scanned across sequential layers of powder material to selectively sinter or melt powder in each layer to form a multilayered part. In selective deposition modeling, a build material is jetted or dropped in discrete droplets, or extruded through a nozzle, such that the build material becomes relatively rigid upon a change in temperature and/or exposure to actinic radiation in order to build up a three-dimensional part in a layerwise fashion.
In film transfer imaging (“FTI”), a film transfers a thin coat of resin to an image plane area where portions of the resin corresponding to the cross-sectional layer of the part are selectively cured with actinic radiation to form one layer of a multilayer part.
Certain SFF techniques require the part be suspended from a supporting surface such as a build pad, a platform, or the like using supports that join the part to the supporting surface. Prior art methods for generating supports are described in U.S. Pat. Nos. 5,595,703; 6,558,606; and 6,797,351, the disclosures of which are incorporated by reference herein in their entirety. However, these prior art supports are not always adequate in certain SFF techniques that exert various external and internal forces on the part being produced and the supports that are supporting the part being produced.
Another shortcoming of prior art support-structure methods for SFF systems is that in most cases they tend to require a large amount of human interaction. Supports determined by existing support structure methods and software need to be inspected and edited manually before starting a build to ensure all the required areas are supported. This is a significant problem because it requires a large amount of human interaction even for an experienced user to edit the supports. This drastically reduces the throughput of a SFF system that has inherently being designed to be fast, quick, easy-to-use and office-friendly.
Yet another shortcoming of prior art support-structure methods for SFF systems is the creation of excessive support structures or not enough support structures. In addition, the supports may not support the exact part geometries being cured. As a result, there is a likelihood that the supports may not support the exact geometries that are actually being cured by the projected or guided light.
Another potential shortcoming that may occur when using existing stereolithography support structure methods in new solid imaging technologies, such as FTI, is the lack of variation in support geometries. Present-day supports have triangular cross-sections without the thickness varying from bottom to top. As a result, the support thickness is always one pixel wide, which requires that a large number of supports be used to adequately support the part during and after build.